1. Field of the Invention
The present invention relates to the art of non-toxic oxygen transport and contrast enhancement agents, and more particularly to stable emulsions capable of sterilization and suitable for internal and intravenous animal, including human, use where the emulsion is a brominated perfluorocarbon in the discontinuous phase in the presence of certain what are believed to be stabilizing agents.
2. Description of the Prior Art
Mono-brominated cyclic and acyclic perfluorocarbons in aqueous emulsions with a minor amount of an emulsifying agent have been known for medical applications involving animals, including humans, for both radiopacity and oxygen delivery. Oxygen is highly soluble in, for example, perfluoroctylbromides. See Long, U.S. letters Pat. No. 3,818,229; No. 3,975,512; and, No. 4,073,879. The present invention is directed toward improvements in the use of such bromofluorocarbons wherein the oxygen transport characteristics, as well as the storage characteristics of the emulsions are enhanced, while the toxicity is further minimized or decreased altogether.
In the past, efforts to use emulsified fluorocarbons as an oxygen transport or carrier, as in a blood substitute, have encountered certain difficulties. Purity, non-toxicity, chemical and biological inertness and excretability are necessary objectives. The emulsified fluorocarbon must be capable of sterilization, preferably by heat, have long-term size and function stability in the fluid or non-frozen state, be industrially feasible, persist for sufficiently long times in the blood stream when used intravascularly and be eliminated rapidly from the body. It has been conventionally believed that those fluorocarbons which have fast elimination times from the body do not form stable emulsions, and that those fluorocarbons which form stable emulsions are retained too long in the body. Non-brominated perfluorocarbons show a direct relationship between emulsion stability and molecular weight and an inverse relationship between molecular weight and excretion rates from the animal body. Both types of fluorocarbons are inadequate, and attempts to combine amounts of both types have merely combined the problems of each.
For intravenous use, it is considered important to have small particle size. However, long term storage for extended periods of time for a month and longer, of fluorocarbon blood substitutes, or "synthetic blood" has heretofore resulted in conglomeration of the fluorocarbon particles of the emulsion into larger particles, especially after heat sterilization. For a general discussion of the objectives and a review of the efforts and problems in achieving these objectives in fluorocarbon blood substitutes, see "Reassessment of Criteria for the Selection of Perfluoro Chemicals for Second-Generation Blood Substitutes: Analysis of Structure/Property Relationship" by Jean G. Riess, 8 Artificial Organs, 34-56 (1984).
Larger particle sizes are dangerous in intravenous use in that they tend to collect in the lung, spleen and some other organs, enlarging them and endangering their functioning. On the other hand, it is desired to have sufficient particle size in the fluorocarbon particles for them to collect in tumors and other areas when the fluorocarbons are used as a contrast enhancement medium. Larger particle sizes, also, are unobjectinable when used in other, non-venous systems in the body, such as, for example, the cerebrospinal fluid ventricles and cavities.